This invention relates to an apparatus for preventing the imposition of excess unidirectional torque upon a rotating drive line.
In many applications where high-powered drive means are utilized to cause rotation of control devices, valves, and the like, means must be provided for causing the source of power to interrupt when the torque imposed upon the system exceeds a permissible limit. For example, a large fluid flow-control valve might be operated by means of heavy-duty screw gear which, when turned in one direction opens the valve and, when turned in the opposite direction, closes the valve. Depending upon the size of the valve and the operating screw gear, tremendous torque levels can be required to respectively open and close the valve and the torque requirements for the opening and closing operations can be substantially different. In such valves, which are usually motor driven, means for limiting the torque imposed upon the mechanism must be provided to prevent breakage of the components.
In the past, torque limitation was provided by devices such as that illustrated in U.S. Pat. No. 3,124,227 to Helland et al. The automatically resetting Helland device operates quite satisfactorily in installations requiring bi-directional torque limitation. However, the prior art systems are not practical where the torque requirements of the operating device are different for each of the two rotational directions; e.g., where the torque required to close a valve is much greater than that required to open it.
This invention is directed to improvements in the prior art systems, such as the Helland device, for use in this particular application. The present invention provides a mechanism which disconnects power to a drive line upon occurrence of an excess torque condition when the driven device is operating in one direction but which permits continued operation in the opposite direction notwithstanding torque conditions.
To accomplish its purposes, the present invention utilizes a mating pawl and groove, mounted in a rotor and housing respectively, and utilizes pin and slider means to permit resilient pivoting of the pawl out of the groove when the unit rotates in one direction while preventing pawl movement when the unit rotates in the opposite direction.
The inventive system has a rotor which is splined or otherwise connected to one portion of a drive line. It also includes a housing, coaxial with the rotor, which is connected to another portion of the drive line and into which the rotor fits. The rotor is equipped with a pivotable pawl and with a pair of spring biased slide members which bear upon opposite sides of the pawl and resiliently bias it normally into a neutral position in which it engages an elongated groove in the housing.
One of the slide members is provided with a pin-receiving cut-out portion. A rigid pin, fixed to a portion of the rotor, is provided immediately adjacent to the pawl and received within the cut-out portion of the slide member. The rotor has a head portion with a plurality of cam surfaces thereon. The housing is equipped with a pair of push rods with tip or end portions adopted for engagement with the rotor head cam surfaces. The rods are fixed for movement with a collar member which is concentrically slidibly mounted on a portion of the housing. The collar member is spring biased into firm contact with the housing and is axially slidable away from the housing and into contact with a disconnect control device when the rotor cam surfaces bear against the tips of the push rods.
The primary object of the present invention is to provide an apparatus which, when inserted in a drive line, will disconnect power to the drive line when a predetermined excess torque condition is reached.
Another object of the present invention is to provide a drive line torque limiter which will disconnect power to the drive line upon an excess torque condition only when the drive line is rotating in one direction.
A further object of the present invention is to provide a compact one-way torque limiting apparatus having a resiliently biased, automatically centering operational component.
Other objects and advantages of the present invention will become apparent from the following drawing and description.
The accompanying drawing shows, by way of illustration, the preferred embodiments of the present invention and the principles thereof. It should be recognized that other embodiments of the invention, applying the same or equivalent principles, may be used and that structural changes may be made as desired by those skilled in the art without departing from the spirit of the invention.